# Questions tagged [geometry]

(1) abstract geometry; (2) storing geographic data in projected coordinates; (3) a generic ESRI term for vector features; a class for "geometry" objects.

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### What are Definition, Algorithms and Practical Solutions for Concave Hull? [closed]

Convex Hull A convex hull of a shape is defined as: In mathematics, the convex hull or convex envelope for a set of points X in a real vector space V is the minimal convex set containing X (...
70k views

### Finding minimum-area-rectangle for given points?

As you see in the figure, the question is: How to find the minimum-area-rectangle (MAR) fitted on the given points? and a supporting question is: Is there any analytical solution for the ...
35k views

### Visualising WKT geometry string in QGIS

A very simple question: Is there a simple tool in QGIS to graphically visualise geometry formatted as text? Example geometry: "POLYGON((571178 6337246,571178 6402217,598061 6402217,598061 ...
126k views

### Getting coordinates from geometry in PostGIS?

This line: SELECT geom FROM myLayer.geom will return a hex value. How would I get decimal values, which is a human-readable coordination?
34k views

### Finding center of geometry of object?

Given a set of 2D or 3D points: How to find the center of geometry of an object? According to the following figure, the center of geometry differs from the center of mass if it is calculated in the ...
37k views

### Fixing geometry validity errors in QGIS?

I am working on ownership data at a US county level. I have one shapefile per county that contains thousands of tax parcels. I need to dissolve the polygons representing parcels owned by the same ...
75k views

### Create a geography/geometry column from x and y fields - SQL Server 2008

I'm new in SQL Server 2008 and I hope you will understand my question/need. Thus, I have a table which contains 3 fields (Name, Lat and Long) in my data base (spatial). I want to create a geometry/...
9k views

### How to store lines and polygons in JSON documents?

Looking at the increasing NoSQL movement and considering that databases like MongoDB offers a new perspective in flexible data storage for GIS. What is the best way to store lines and polygons in ...
32k views

### Converting GeoJSON to Python objects? [closed]

New to the site, and to geoJSON, and to python. My goal is to read in a file with geoJSON data, and use it to generate shapes to be used in an application that is using python scripting. Python ...
946 views

### Space filling between random 2D lines

Consider a region (2D) filled with lines randomly (following Figure). We are interested in filling the empty spaces between lines including four boundary edges in a way: 0- maximizing the size of ...
11k views

### Seeking Generalisation Strategies for Building Outlines in PostGIS?

I have a dataset of building footprints vectorised from a raster dataset. The dataset is currently just a vector representation of the raster data. I would like a polygon dataset that only has ...
10k views

### How can I find a point inside a polygon in PostGIS?

How can I find a point that is guaranteed to be within a given polygon in PostGIS? I am aware of the ST_Centroid function. However, the centroid is not always within a polygon, see below: ...
59k views

### Convert shapefile to CSV including attributes AND geometry?

I have a shapefile with 60k+ entries, all of which are polygons with corresponding attributes (acreage totals, landowner names, tax ID #s, etc.). What I ultimately need is a CSV file with all of ...
19k views

### Storing GeoJSON FeatureCollection to PostgreSQL with PostGIS?

I am new to GeoJSON. I have a GeoJSON features collection as shown and would like to store it in postgres table (testtable). My postgres table has a serial id and geometry column. { "type": "...
4k views

### How is ST_PointOnSurface calculated?

The PostGIS documentation states that ST_PointOnSurface returns "a POINT guaranteed to lie on the surface". It seems like this function could be trivially implemented to give results that satisfy the ...
15k views

### How to find the maximum-area-rectangle inside a convex polygon?

In this post we are looking for algorithms / ideas on how to find the maximum-area-rectangle inside a convex polygon. In the following figure, numbers are the areas of the fitted rectangles. As shown ...
3k views

### What is the precision of SELECT DISTINCT on PostGIS geometry column?

I wonder what the precision of the SELECT DISTINCT operator is on a PostGIS geometry. On my system, the following query gives me a count of 5, which means that the inserted points are considered equal ...
6k views

### How to calculate the angle at which two lines intersect in PostGIS?

I want to calculate the angle between two lines where they intersect in PostGIS. The starting point for angle calculations in PostGIS seems to be ST_Azimuth - but that takes points as input. My first ...
8k views

### Finding tunnel center line?

I have some map files consisting of 'polylines' (each line is just a list of vertices) representing tunnels, and I want to try and find the tunnel 'center line' (shown, roughly, in red below). I've ...
5k views

### Comparing two geometries in ArcPy?

I am trying to compare two separate feature classes to identify differences between them (sort of a diff function). My basic workflow: I extract the geometries using a SearchCursor Save the ...
12k views

### Converting between Esri Geometry and WKT using ArcObjects?

It seems like there is no means of converting an ArcObjects geometry to the Well-Known Text representation (and vice versa) in ArcGIS ArcObjects API. The only thing I was able to find is conversion to ...
10k views

### Postgis - Converting 'geometry_dump' data type to a 'geometry' type

I am working with a dataset of property boundaries that has had ST_Union() run on it, thus all the polygons appear as a multi polygon in one row of a table. I would like to separate these out so I get ...
23k views

### Copy a geometry from one feature to another without attributes?

With QGIS it's easy to add a new part to an existing feature/geometry but I can't see how to copy/paste this part from another existing feature/geometry. Is it possible?
610 views

### Terminology: Polygon or Area?

When writing about GIS geometry I'm unsure whether to use the term "polygon" or "area". In particular, does the word "polygon" suggest a specific type of geometry? For example, a colleague suggested ...
39k views

### How I get SRID from Geometry field

What is the function for getting SRID from Geometry field. I have inserted a shapefile into SQL Server table with a Geometry field defined. I know the projection of shapefile is Swreff99_1800 (EPSG:...
42k views

### Removing duplicate features with same geometry in ArcMap?

Is it possible to uniquely identify each geometry in a feature layer? Essentially I have a polygon feature layer with many rows of data represented by the same geometry. I would like 1 row for each ...
11k views

### Correcting gaps and overlapping polygon (parcels) geometry

I have come across a resource that we rely upon almost daily that is in terrible need of repair. It is not our own product and the supplier is generally not interested in fixing the problem. We are ...
12k views

### Exporting only certain columns to CSV file in ArcGIS for Desktop?

I've written a python script using arcpy which outputs a polygon feature class into a File Geodatabase. I have added a function to export the attributes to a separate CSV file. I am using the code ...
11k views

### How to draw polygons from the python console?

I've been visiting and revisiting the page on geometry handling in the PyQGIS Cookbook: http://documentation.qgis.org/2.0/en/docs/pyqgis_developer_cookbook/geometry.html but can't seem to figure out ...
579 views

### What in-depth spatial database systems tutorials exist? [closed]

Is there a good tutorial that explains in depth the internals of a GIS and a spatial database system such as PostGIS with examples and without any background assumption? I'm specifically looking for ...
6k views

### Inverting Polygons using QGIS?

I have a Shapefile with Polygon features representing the world's land areas (continents, islands). Is it possible to invert these, and get a geometry that represents the world's oceans and seas? ...
2k views

### How to snap a road network to a hexagonal grid in QGIS?

I'm trying to use QGIS 2.14 to snap a road network to a hexagonal grid, but I'm getting strange artifacts. I've created a hex grid with MMQGIS, cells are approx 20 x 23 m. I've buffered the road ...
3k views

### Centroid coordinates for odd-shaped polygons

I have a problem in computing the centroids of certain polygons in QGIS (via the geometry tools): for certain polygons - with a strange and rather long shape - the centroids computed are off the ...
1k views

### Simulating the expansion of polygon features

I've got what I'm hoping will be an interesting question. I'm working on an assignment for an intro to GIS course that uses some Gulf oil spill data to introduce common vector-based spatial analysis ...
544 views

### Detecting branched polygon shape?

I have a vector layer with millions of polygons making continuous coverage. I need to classify them according to their shape. I am already using several shape indexes from landscape ecology like ...
9k views

### Self intersections for polygons, how to solve?

I have a question about repairing a self intersecting polygon shapefile. I have a shapefile containing Polygons (ZM) which have self intersecting features. If I use the "repair geometry" tool, it ...
1k views

### Difference between geometry and \$geometry QGIS

This may be trivial question, but I'm confused, what is the difference between geometry and \$geometry in QGIS? I didn't find any examples of using this function. Particularly I'm interested in ...
10k views

### Multipoint vs point PostGIS

Is it normal to use the geometry type 'multipoint' instead of 'point' knowing that I use it to store only one point? How can I convert from multipoint to point?
1k views

### How big does a circular geofence need to be for the curvature of the earth to matter? [duplicate]

I'm working on adding geofences to a mobile application. I know the proper way of calculating distance between two points on a sphere is using the great-circle or Haversine formula. I don't know if ...
560 views

### Alter Minimum Bounding Box Algorithm

I'm trying to create an algorithm similar to minimum bounding box (though it may end up looking nothing like it). In this case the angle will be passed as a parameter and given the angle I need the ...
412 views

### Why do file geodatabase and SDE readers produce different fme_geometry types? [closed]

I have one very simple workbench that I am running against both SDE (9.3) and FGDB (10.0) sources. I noticed two different fme_geometry values for same type of objects. For the first one, i.e SDE 9....
3k views

### What are the implications of invalid geometries

I've imported some data in a Postgis database and some of the geometries are reported invalid (ST_IsValidReason reports self-intersection or ring self-intersection). The queries I am performing don't ...
8k views

### Creating line of varying distance from origin point using Python in ArcGIS Desktop?

I'm trying to create a line feature from a single point, using a set distance and angle using ArcGIS and Python (ArcPy). I have a point at these coordinates: X = 400460.99, Y = 135836.76 From ...
4k views

### Measuring straightness of a curve segment (represented as a polyline)

I'm working on an automatic elevation contour labeling algorithm and one of the factors that I want to take into account when deciding the positions of labels is how "straight" a particular segment of ...
14k views

### How to convert from SQL Server geometry BLOB to something else?

I have a CSV data file from a 3rd party that is an exported SQL Server table. They simply did a select * from foo and output the result to a text file and sent it over. In their table is column of ...
17k views

### Creating lines from points pair coordinates with ArcPy?

I've got some points pair coordinates (start and end points) which I have to transform into lines. Until now, I used an append of both the coordinates in a pippo.Point(), a pippo.CalculateGeometry() ...
6k views

### Cutting up a shapefile into smaller parts

I've downloaded the 450MB coastline shapefile from OpenStreetMap, I want to split it up in smaller parts. Is there a way to generate a shapefile with only the polygons contained in a smaller area? ...
6k views

### Calculating a spherical polygon centroid

I'd like a general way to calculate centroids for polygons on a sphere. So far, the best online reference appears to be: Tools for Graphics and Shapes by Jeff Jenness. The method described there ...